Tungsten film deposition using chemical vapor deposition techniques is an integral part of semiconductor fabrication processes. Tungsten films may be used as low resistivity electrical connections in the form of horizontal interconnects, vias between adjacent metal layers, and contacts between a first metal layer and the devices on a silicon substrate. In a conventional tungsten deposition process, a barrier layer is deposited on a dielectric substrate, followed by deposition of a nucleation or seed layer of tungsten film. Thereafter, the remainder of the tungsten film is deposited on the nucleation layer as a bulk layer. Conventionally, the tungsten bulk layer is formed by the reduction of tungsten hexafluoride (WF6) with hydrogen (H2) in a chemical vapor deposition (CVD) process.
As semiconductor devices scale to smaller and smaller technology nodes, shrinking contact and via dimensions make CVD of tungsten more challenging. Increasing aspect ratios can lead to voids or large seams within device features, resulting in lower yields and decreased performance in microprocessor and memory chips. Void-free fill in high aspect ratio features of 10:1, 20:1 or greater is difficult using conventional CVD tungsten deposition techniques.